Method of providing retro-reflective stripes on cylindrical surfaces

ABSTRACT

A METHOD OF MARKING CANS WITH A REFLEX-REFLECTING STRIPE TO AFFORD MORE RELIABLE SORTING OF CANS IN A CANNERY. THE METHOD COMPRISES OF THE APPLICATION OF A THIN NARROW STRIPE OF A SOLVENT-CONTAINING ADHESIVE COMPOSITION TO THE CAN SURFACE, DRYING THE STRIPE TO DEVELOP A HIGHLY TACKY STRIPE ON THE CAN, APPLYING A MONOLAYER OF GLASS SPHERES TO THE STRIPE TO HOLD THE SPHERES ON THE CAN, AND PERMITTING A FURTHER DRYING OF THE COMPOSITION TO A TACK-FREE STATE. THE SOFTENING POINT OF THE COMPOSITION IN THE TACK-FREE STATE SHOULD BE AT LEAST 260*F.

Feb. 16, 1971 M. L. JOH ON 3,563,781 METHOD OF PROVIDING RO-REFLECTIVE STRIPES ON INDRICAL SURFACES I Filed c. 11, 1967 56.4

I N VEN TOR.

y MELW/VLJO/f/YSO/V United States Patent 3,563,781 METHOD OF PROVIDING RETRO-REFLECTIVE STRIPES 0N CYLINDRICAL SURFACES Melvin L. Johnson, St. Paul, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul,

Minn., a corporation of Delaware Filed Dec. 11, 1967, Ser. No. 689,709 Int. Cl. B44c 1/00, 1/16 U.S. Cl. 117-18 5 Claims ABSTRACT OF THE DISCLOSURE A method of marking cans with a reflex-reflecting stripe to afford more reliable sorting of cans in a cannery. The method comprises the application of a thin narrow stripe of a solvent-containing adhesive composition to the can surface, drying the stripe to develop a highly tacky stripe on the can, applying a monolayer of glass spheres to the stripe to hold the spheres on the can, and permitting a further drying of the composition to a tack-free state. The softening point of the composition in the tack-free state should be at least 260 F.

The present invention relates to a method of placing a reflex-reflecting stripe on cylindrical objects, and in one respect relates to a method of applying a continuous or discontinous stripe around a cylindrical object such as a can such that the same may be sorted after the processing of it in a cannery with foodstuffs, fruits, etc., therein.

It has been found to be necessary to apply markings to cans in the canning industry to afford a means for sorting cans after they have been filled and sealed but before identifying labels are applied thereto. The sorting is necessary to sort two or more different quality grades of foodstuffs or to sort different foodstuffs which are canned and cooked or processed simultaneously. This sorting operation is generally done after the cans leave the continuous cookers in the canning plant and it is therefore necessary to imprint onto the can some identifying mark prior to the cans being filled and sealed, which mark will remain on the cans and afford a sure method of sorting when the products leave the cooker and before the identifying labels are applied.

Previous to the present invention, the identifying marks on the cans have often been a black ink band which completely encircles the can body. The can bodies containing different products are marked with bands having different axial locations along the cylindrical can body. These ink bands may be placed upon the can by a stencil or imprinted on the can body by a printing roll which carries ink to and transfers the same to the surface of the can body. These black rings or ink bands are then used for sorting in different sorting machines where the presence of the circumferential mark at a predetermined height or location along the cylindrical can body or the absence of the mark is the means by which the different products or grades of products can be segregated. With these ink bands, photocells are positioned to respond to variations in intensity of light reflected from each can body passing in a single file, and the cans are sorted because the photocell either fails to receive any reflected light due to the presence of the black band or it sorts the can because of the absence of the black band and the reception of reflected light in the photocell.

The difficulty with this type of coding system for the cans is that during the handling of the cans to carry out the usual operations of filling, sealing, cooking, and conveying, the ink band becomes marred causing removal of part of the ink from the can. The marred area then permits the light from the lighting source to reflect therefrom to the photocell, thus mistakenly reading the code on a can such that there is a likelihood that a can of peach halves could be labeled as diced peaches. Also, where there is no mark on the can and reflected light should be received, the can may possibly be dented such that the surface presented to the light does not present the anticipated reflection. The can then passes as one with a dark band.

It has therefore become evident that an improved marking for the can is necessary to ensure the sorting operation desired. The present invention fulfills this need. It is accomplished by the application of a continuous retro-reflective stripe to the can or discontinuous, interrupted retro-reflective stripes. The stripes or marks ensure proper sorting. They afford more positive sorting than the measuring of changes in the intensity of reflected light. Retro-reflective marks permit the cans to be scanned by the sorter over a wider angle, approximately 4 the circumference of the can. It has been difficult however to apply a retro-reflective stripe or mark to the cylindrical bodies by a system which will be reliable to assure the results desired and which will be convenient and economical.

Prior to the present invention experiments were made by applicant using a hot melt thermoplastic adhesive composition to serve as a binder for supporting retroreflective beads or spheres on a can. With this earliertried system the adhesive had to be brought to a molten state satisfactory for coating. For a composition which would not become softened during the time the can is in the cooker, the melting point of the composition had to be so high it required a high temperature in the pot of adhesive at the applicating station. This is undesirable in that an operator making adjustments on the coating equipment could easily be burned. Further, it is necessary to heat the cans as they are carried to the applicator to prevent too rapid a cooling of the coated band before the glass beads are applied. This adds another hazard and increased expanse to the system. Additionally, the maintenance on the pot for the hot melt adhesive is increased. For these reasons the problem was unsolved prior to the present invention.

The present invention provides a method for applying a retro-reflective stripe to a can body which will afford retro-reflectance of the light from the light source to a meter or photocell, or alternatively no reflectance to the photocell, depending upon whether a stripe, as obtained from the practice of the present invention, is present or not at the desired location on the can body surface.

The present invention provides a method of obtaining a satisfactory retro-reflective mark on the can which is less troublesome and more economical than earlier-tried methods.

The present invention provides a method of applying a reflex-reflecting stripe to a can body to permit the sorting of cans, which stripe will withstand the heat of the cooker, and other abuse in the canning process.

The method of the present invention provides for the marking of a can body by applying a reflex-reflective mark thereon by means of first applying a thin strip of a solvent-containing adhesive composition on the can body and then applying to the adhesive strip a layer of particles while the adhesive material is in a tacky state, to form on said can body a reflex-reflective stripe which is not rendered ineffective through the cooker and canning processes.

An apparatus for practicing this invention is described below and is shown in the accompanying drawing. An improved apparatus is described and claimed in U.S. Pat. No. 3,424,127 issued to Melvin L. Johnson and Arnold P. LeVasseur, and it is incorporated herein by reference.

The above and further advantages and features of the 3 present invention will become more apparent after reading the following detailed description which also refers to the accompanying drawing wherein:

FIG. 1 is a schematic view of an apparatus for practic ing the method;

FIG. 2 is a perspective view illustrating a can marked with a continuous and discontinuous mark;

FIG. 3 is an enlarged fragmentary sectional view of a can surface and the retro-reflective stripe; and

FIG. 4 is an end view of a coating Wheel with a discontinuous peripheral surface.

Referring now to the accompanying drawing, there is shown in FIG. 1 an apparatus formed to carry out the method of the present invention. The apparatus comprises a first station 5 into which the cans 6 are moved in sequential spaced relation to receive a band of an adhesive composition. The cans 6 move by gravity to a star Wheel 7 which is rotatable to advance the cans into a circuitous path defined by a guide 8 and a narrow coating roller 9. The coating roller 9 has an outer peripheral band or tire adapted to carry and transfer the adhesive composition. The band is preferably resilient to permit contact with the can, e.g., a silicone elastomer, and engages the can 6 and rolls it along guide 8 and thus rotates the can through one revolution to simultaneously apply thereto a continuous band of adhesive composition about the can. The adhesive composition is picked up by the roller 9 which is partially immersed in a supply of adhesive composition placed in a container 12. A doctor blade 10 is placed near the outer periphery of the roller 9 to control the amount of adhesive carried into contact with the can surface. The roller 9 is suitably driven to afford the transfer of adhesive composition.

After being coated with the adhesive composition the can is moved to a second station 13. In moving to the second station the can moves along a guide 14 connecting the stations. During the interval the can is moving between stations the adhesive composition must be dried to an extent rendering the band tacky so it will pick up the dry lens elements or reflex-reflective particles. The drying is accomplished by the solvent evaporation. A source of hot air may be directed at the can body or, as illustrated, a relative long guide 14 can be used so the can is moved through the ambient air to sufliciently dry the adhesive composition to the tacky state.

At station 13 the can 6 is moved by a rotating star wheel 16 into contact with an applicating roller 17 which rotates the can along a guide 18. The extent of guide 18 is sufficient to rotate the can through one revolution before the can separates from the periphery of the roller 17. The roller 17 is positioned axially to be aligned with the band of adhesive placed on the can by roller 9. Thus the roller 17 and the roller 9 are disposed in a single plane.

The reflex-reflective particles are stored in a supply container 19 which may be provided with suitable agitating means or vibrating means to keep the particles from blocking. A transfer roller 21 carries the particles from the container 19 into contact with the applicating roller 17. The roller 17 and transfer roller 21 have continuous peripheral surface coatings of a silicone elastomer which will carry a monolayer of the particles and by contact between rollers 17 and 21, the particles will be transferred from the roller 21 to the roller 17, whereupon they will be transferred to the tacky adhesive stripe on the cans 6 while the same is still tacky. The adhesive stripe will lift the particles from the roller 17 and bind the same to the can.

A marked can illustrating two stripes is illustrated in FIG. 2. The continuous reflex-reflective stripe 22 extends completely around the surface of the can and upon further drying of the adhesive composition the stripe will withstand the abuse it is subjected to during further processing in the cannery.

The mark is shown more clearly in FIG. 3 with the adhesive or binder material 23 adhered to the can 6 and a monolayer of reflex-reflective particles 24 set in the material.

FIG. 4 illustrates an applicating roller 26 having an outer peripheral band or tire 27 with a discontinuous surface because of the presence of axially extending circumferentially spaced slots 28 providing an applicating surface affording stripes approximately A inch long and spaced approximately /2 inch apart around the can. A roller such as 2 6 can be substituted for either roller 9 or 17. When a continuous stripe of adhesive composition is applied the lens elements or spheres are applied to spaced areas. If the adhesive composition is applied in the intermittent pattern the spheres are applied by a contmuous surfaced roller to ensure the placement of the spheres on each stripe of adhesive. A discontinuous stripe 29 is illustrated in FIG. 2 with a continuous band of adhesive material and lens elements or spheres applied in short spaced intervals.

The above-described apparatus thus performs the task of applying a reflex-reflective stripe on the cylindrical surface of a can. The process consists of applying a th1n continuous or intermittent coating of adhesive or hinder material of a desired width around the can body. Secondly, while the adhesive material is still tacky, the lens elements or reflex-reflective particles are placed in contact with the adhesive material to coat portions or substantially all of the adhesive stripe.

The lens elements or reflex-reflective particles 24 may be tiny glass spheres, with an index of refraction in the 1.8-2.1 range, and from 20 to 100 microns in diameter, preferably 3050 microns, placed in a binder which contains material affording a reflective property. Such reflective property is provided by materials such as aluminum flake or paste, a bronze flake or other metallic flake or powder. Titanium dioxide pigment or other commonly used white pigment could also serve as a reflective material in the binder supporting the particles.

A preferred system is to use glass spheres which have been hemispherically coated with a reflective material. These particles randomly applied to an adhesive band will provide a good reflex-reflective stripe. The binder then need not contain any material making it reflective. Such spheres or reflex-reflective elements consist essentially of glass spheres of about 1.8-2.1 refractive index with hemispheric coatings of reflective metal such as silver or aluminum, as are described in the Palmquist and Beck United States Pat. No. 2,963,378, although other types of reflex-reflective elements may be used.

The adhesive or binder is applied directly to the can body. An even coat should be applied and preferably the depth or thickness of the coating should not exceed 40 to of the average size of the dry particles. The application of this material by a single roller from a reservoir as opposed to the use of an intermediate transfer roller, as is characteristic of ink printing, assures a more uniform coating and prevents accumulation of dried or partially dried material forming on the periphery of the adhesive-applying roller.

The adhesive or binder material dissolved or dispersed in solvent to provide a solvent-containing adhesive composition suitable for use in the present invention should have good adhesion to metal and glass while the can is being processed through the canning operations, should resist marring or removal by rubbing when handled at 260 F. or less, should not be softened or become tacky by the presence of water or steam, and it should resist any deleterious effects, e.g., loss of adhesion from additives put in the water or steam such as rust inhibitors or detergents. In a preferred form the binder is also relatively inert. For use with coated glass spheres it is also preferred that the adhesive or binder material be neutral or acidic. The solvent should be an organic solvent having a boiling point at atmospheric pressure below C. and should flash off quickly to provide a residue having high initial tack to permit the transfer of the glass particles to the can, which residue will further dry to a tack-free state. The solvent is preferably relatively nontoxic. In some instances, the solvent may at best in part be a polymerizable monomer which can be polymerized as desired, e.g., by heat, actinic irradiation, electron beam, etc.

Some examples of suitable solvent-containing adhesive compositions adapted to be applied to the cans as a band are:

EXAMPLE I Parts Epon 1010 40.0 Epon 1007 13.5 W W Wood Rosin 3.3 Methyl ethyl ketone 43.2

Epon 1007 is a reaction product of bisphenol A, i.e., [2,2-(4,4'-dihydroxy diphenyl)propane], and epichlorohydrin having an epoxy equivalent weight of 2,000-2,500, a Gardner-Holdt viscosity at 40% solids by weight in Dowanol DB 25 C. of YZ and a Durrans softening point of 125-135 C. Epon 1010 is a reaction product of bisphenol A and epichlorohydrin having an epoxy equivalent weight of 4,000-6,500, a viscosity of Z Z a softening point of 155165 C. The W W Wood Rosin is a natural occurring wood rosin, water white grade, consisting primarily of a mixture of abietic acid, dehydroabietic acid and isomerized dehydroabietic acids with an acid number of 164, a nonsaponifiable value of 6.5%, a

softening point (Ring and Ball) of 163 F.

EXAMPLE II Parts Emerez 1533 37.5 Cymel 248-8 & between 12% PTSA 6.5 RBH 510 6.0 Mixed with solvent of Isopropanol 40.0 Toluene 10.0

Emerez 1533 is a polyamide which is derived from diphenolic acid, it has an amine value of 5, an acid value of 2.5, a density of 8.3 lbs. per gallon, and an ASTM test method E2858T softening point of 98102 C. Cymel 248-8 is a resinous heat-reactive condensation product of melamine, formaldehyde, and butanol, available as a solution in a mixture of butanol and xylol. PT SA is paratoluene sulfonic acid and comprises between 1 and 2% of the total mixture with Cymbel 248-8. RBH 510 is a natural hydrocarbon resin of fossil origin, having the following analysis: hydrogen-ll.0%, carb0n87.04%, nitrogen0.96%, sulfur-0.30%, ash0.50%, noncombustible residue slight, halogen and phosphorusnone, average molecular weight-732, acid number 6-8, iodine value 140-150, a softening point of 320 F., a refractive index of 1.544, and it is soluble in aliphatic and aromatic hydrocarbon solvents and insoluble in water and alcohol. RBH-510 is available from RHB Dispersions Division and/or Color and Chemicals Division of Interchemical Corporation, Hawthorne, NJ.

EXAMPLE III Parts Emerez 1533 37.5 Cymel 248-8 & between 12% PTSA 6.5 Cumar W 6.0

Mixed with solvent of Isopropanol 40.0 Toluene 10.0

Emerez 1533 and Cymel 2488 have been previously described. Cumar W is a coumarone-indene resin with a Ring and Ball softening point of 259-277 F. and a Fisher-Johns melting point of 215250 F. Cumar W is available from the Plastics and Coal Chemical Division of Allied Chemical Corporation.

6 EXAMPLE IV Parts Kraton 101 25.0 Cumar W 25.0 Toluene 50.0

Kraton 101 is a polystyerene-polybutadiene-polystyrenetype block copolymer wherein the central polybutadiene block has a molecular weight of 60,000-100,000 and each of the two terminal polystyrene blocks has a molecular weight of 10,000 to 20,000 Cumar W is defined above.

EXAMPLE V This example of the adhesive composition is for use with uncoated glass spheres in a size range of from alout 20 to microns, preferably 30-50 microns and provides a reflective binder for the beads to afford the reflexreflective property to the completed stripe.

Parts by wt. Epon 1010 42.10 Epon 1007 14.12 W W Rosin 3.47 MD 566 aluminum paste 10.00 Methyl ethyl ketone 45.47

MD 566 standard luster aluminum paste is available from Metals Disintegrating Company, Inc. and has a solids content of binder and aluminum flake of 74.0% in a hydrocarbon thinner size 99.0% through 325 mesh, approximate specific gravity 1. 65, approximate flaking value 65%, approximate covering on water of dry flake 18,000 square centimeters per gram, and bulking value of 0.073 gallon per pound.

The efliciency of this system to provide retro-reflectance is lower than with the use of reflective metal hemispherically coated beads, but is satisfactory for can sorting.

The adhesive material may thus be thermosetting or thermoplastic, the latter affording less maintenance on the pot 56. Preferably the resins are sufficiently soluble to produce solutions with a solids content of 40% or greater and they should be soluble in common, highly volatile solvents such as methyl ethyl ketone, toluene, ethyl acetate etc.

Having thus described the present invention what is claimed is:

1. A method for marking a cylindrical metal can with a retro-reflective stripe that permits automatic sorting of the can by photoelectric sensing means, said method for marking comprising the steps of (1) rotating the can at least once about its axis while simultaneously applying around the circumference of the can a narrow thin stripe of an adhesive composition that comprises (a) a highly volatile solvent that boils at a temperature below 212 F. and quickly flashes from a thin layer of the adhesive composition, and (b) an adhesive binder that forms a nontacky film that has a softening point of at least 260 F. and does not soften nor become tacky in the presence of water or steam, the stripe of adhesive composition first becoming highly tacky as the solvent flashes off and then becoming dry and nontacky as the adhesive binder is converted to its nontacky state,

(2) advancing the stripe of adhesive composition to a tacky condition, and

(3) subsequently rotating the can about its axis again *while the adhesive stripe is in the tacky condition, and simultaneously transferring to the surface of the stripe a monolayer of transparent glass spheres that are between about 20 and 100 microns in diameter.

2. The method of claim 1 wherein said reflex-reflecting particles are glass spheres hemispherically coated with a reflective metal.

3. A method for marking a cylindrical container with a retro-reflective stripe that permits automatic sorting of the container by photoelectric sensing means as the container travels along a conveyor, said method for marking comprising the steps of (1) rotating the container at least once about its longitudinal axis while simultaneously applying a stripe of adhesive composition at one or more selected locations on the side of the container;

(2) subjecting the stripe of adhesive composition to conditions such that the adhesive composition first becomes highly tacky and then becomes dry and nontacky;

(3) forming on the surface of an applicator roller a monolayer of glass spheres that are between 20 and 100 microns in diameter and are releasably held on the surface of the applicator roller; and

(4) rotating the container about its longitudinal axis again while the stripe of adhesive composition is in said tacky condition and simultaneously pressing said monolayer of glass spheres on the applicator roller against the stripe to thereby transfer the glass spheres to the stripe.

4. The method of claim 3 wherein said spheres are hemispherically coated with a reflective metal.

5. The method of claim 3 wherein said adhesive composition includes a material to render the dried composition reflective.

References Cited UNITED STATES PATENTS 2,015,658 10/1935 Bezzenberger 1l7-25 2,395,267 2/1946 Gilbert 1l718X 2,430,710 11/1947 Dunlap 11725X 2,496,070 1/1950 Selsky 1l718X 2,723,918 11/1955 Nichols 11743X 2,806,803 9/1957 Thackara et al 1l718X 2,952,192 9/1960 Nagin 941.5 3,016,875 1/1962 Ballentine et al. 1l718X 3,023,121 2/1962 Dyar 1l718 3,246,629 4/1966 Shelffo et a1 1l718X 3,326,098 6/1967 Boettler 941.5X 3,420,597 1/1969 Nellessen et al. 117-27 FOREIGN PATENTS 728,517 4/1955 Great Britain 117-43 WILLIAM D. MARTIN, Primary Examiner US. Cl. X.R. 11725, 27, 43 

